1. Field of the Invention
The present invention relates to an optical apparatus such as a digital camera and an interchangeable lens, and in particular relates to an optical apparatus having a function of moving a focus lens in an optical axis direction to reduce “focus shake” generated in the optical axis direction.
2. Description of the Related Art
Optical apparatuses used for image pickup generally have a so-called image stabilization function to reduce image shake caused by camera shake such as hand jiggling. The camera shake is detected using a shake detection sensor such as an angular velocity sensor and an acceleration sensor. The image shake caused by angular camera shake (camera shake in a pitch direction and a yaw direction) is reduced by shifting part of an image pickup optical system in a direction orthogonal to the optical axis direction according to a detection result by the shake detection sensor.
When a user holds a camera by hand and performs image pickup with a high image pickup magnification such as macro image pickup, defocusing from an object may occur due to a small shake in the optical axis direction (that is, “focus shake”) of the camera since a depth of field of the image pickup optical system becomes small. Such focus shake can be corrected by moving a focus lens in the optical axis direction according to variations of a focus state detected by a focus detection unit.
However, in a single lens reflex camera including a quick return mirror, the quick return mirror is moved out of an image pickup optical path in a period from a time point of a switch operation (for example, a second stroke operation of a release button) for instructing start of exposure to a time point of an open operation of a shutter for starting the exposure. The movement of the quick return mirror out of the image pickup optical path disables detection of the focus state since light from the object does not reach the focus detection unit.
Japanese patent No. 3799666 discloses a camera which has a displacement sensor that detects displacements of the camera in an optical axis direction, and which moves a focus lens included in an image pickup optical system on the basis of a detection result by a focus detection unit and also moves the focus lens during exposure on the basis of a detection result by the displacement sensor.
Moreover, Japanese Patent Laid-Open No. 2006-162682 discloses a camera which performs focus detection by a focus detection unit plural times before a start instruction of exposure, and which starts drive of a focus lens before start of exposure on the basis of a result of the last focus detection.
However, to move the focus lens during the exposure as disclosed in Japanese patent No. 3799666, it is necessary that a magnification of the image pickup optical system be not changed by the movement of the focus lens. In other words, a method disclosed in Japanese patent No. 3799666 cannot be used for an optical apparatus whose image pickup magnification is varied by the movement of the focus lens.
Further, even if using the result of the last focus detection in the plural focus detections performed before the start instruction of exposure as disclosed in Japanese Patent Laid-Open No. 2006-162682, the focus shake occurring before start of exposure may affect a captured image.